Interaction of ambient NH₃ with other trace gases (NO, NO₂, O₃ & CO) and meteorology in a suburban environment of the western Himalaya

Ammonia (NH₃) is the only alkaline N species in the atmosphere, which plays a vital role in several environmental processes and in forming the fine particulate matter through gas-to-particle conversion under favourable meteorological conditions. In the present study, the concentrations of ambient NH₃, NO, NO₂, O₃ and CO were monitored along with meteorology at Palampur, Himachal Pradesh (HP), over the western Himalayan region of India to study the relationship of NH₃ with other trace gases (O₃, NO, NO₂ and CO) and their possible sources over the region from January 2015 to December 2019. The mean concentrations (± SD at 1σ) of ambient NH₃, NO, NO₂, O₃ and CO were extracted as 12.9±8.7 µg m^-3, 15.2±11.5 µg m^-3, 12.9±9.9 µg m^-3, 67.3±22.1 µg m^-3 and 0.42±0.23 µg m^-3, respectively. The concentrations of these trace gases showed significant diurnal, seasonal (maxima in winter and minima in the monsoon) and interannual variation during the study. The concentrations of ambient NH₃ positively correlated with NO, NO₂ and CO in all the seasons, revealing that vehicular exhaust and combustion (other than agriculture) are some of the major sources of ambient NH₃ at the observational site of Palampur. Whereas NH₃ negatively correlated with O₃, it revealed NO_x as well as acidic gas formation (through the oxidation reaction of NH₃ with O₃). The further investigation of the interaction of ambient NH₃ with trace gases (NO, NO₂ and O₃) and meteorology also suggested secondary aerosol formation at the monitoring site of the western Himalaya.